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A.J. Lang, P. Piers, S. Norrby, H. Zhao; Effects of IOL Surface Asphericity on Image Quality in a Pseudophakic Population . Invest. Ophthalmol. Vis. Sci. 2005;46(13):704.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Investigate sensitivity of different IOL asphericities to changes in corneal asphericity, IOL decentration and refractive error. Methods:Finite eye model: cornea conic = –0.14, equiconvex 20D monofocal and 5.5 mm dia. Pupil, raytrace mono light, Feff = 16.3 mm. Image quality metrics: MTF, spherical aberration (Z40), and visual Strehl ratio in frequency domain. Four anterior surface IOL designs (Z40 values with corneal vergence): spherical (0.13), aspheric correcting only the IOL’s aberrations at infinite conjugate (0.07), aspheric fully correcting the corneal aberration (–0.25; e.g., "Tecnis"), and aspheric partially correcting corneal aberrations (–0.06). The image quality versus corneal asphericity in three conditions: a) centered eye model, b) IOL decentered 0.5mm, and c) eye model defocused +0.375D (implant power calculation error). Five corneal asphericities covering population: mean (K = –0.14) plus / minus one and two standard deviations (SD = 0.18). Visual Strehl ratio (VSMTF): integrated product of the MTF and neural CS function, normalized to diffraction, correlates with judgment of best focus. Results:With IOL centered, the fully corrected VSMTF (1.0) exceeded other three designs (avgVSMTF = 0.22). The fully corrected aspheric design is superior for corneal asphericities more positive than about –0.3 or corneas with SA greater than about +0.16 (6.2 mm at cornea). With IOL decentration or slight myopic defocus, all designs have similar VSMTF for corneas with spherical aberration equal or greater than the nominal cornea. Conclusions:The fully cornea correcting aspheric IOL design is the most robust design reducing overall ocular spherical aberration, across corneal population, with IOL decentration and residual refractive error, especially for corneas with SA > Z40 = +0.16 (6.2 mm dia at cornea). Full cornea correcting aspheric IOLs are suggested for subjects with prior corneal Rx procedures tending to increase the SA. The effect on the above trends in the presence of other higher order aberrations, astigmatism, and chromatic aberrations is inconclusive at this point and requires further investigation.
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